PCV valve
 

I have searched and found several posts relating to PCV valves. They don't really answer my question though, which is, Are they really necessary on a built 400/469 mainly for racing but occasional street use. I have open breathers on both valve covers but still has a tendancy to push the dipstick out.

Breathers only don´t pull condensation, blowby gases and contaminating vapors out of the crankcase to keep engine oil clean.

From 1969 Pontiac Service Manual:

Very true.

The early crankcase ventilation systems, "Road Draft Systems", increased the life of the engines several times vs leaving the corrosive gases in the crankcase.
Engine durability on the early engines was poor to be honest.
Today with some maintenance engines can accumulate over 350,000 miles on the vehicle, and still perform well.

"but still has a tendency to push the dipstick out."

It takes significant crankcase pressure to push the typical oil dipstick out of the Pontiac
dip stick guide housing. Sounds like you have a poor sealing (rings?) engine under higher rpm conditions.

Tom V.

Even if your ring seal is ok the pistons pump as much air volume around the crankcase as they draw in on there top side, and collectively they pressurize that air which then needs to go somewhere!

When each one of your pistons desend’s the bore of your 461, there also moving 57 cid worth of air!

Sealing up the open lifter valley of a factory block only makes it more difficult for the air volume to get out to the valve cover area and the very small passage that even two valve cover breathers have can not handle moving that air volume thru them!

For now a quick fix is to hose clamp on a blocked off Carb vacuum cap to the dip stick tube until you need to check the oil.
I would perform a leak down test and hope for numbers of 5% or less which is what a race motor should have otherwise your kidding yourself!

If this pans out then I would be looking into a vacuum pan system.

will a mopar breather routed to the air cleaner help him at WOT?

My opinion: If you want to prevent pressuring up the oil pan area and pushing the dipstick out, run a vacuum pump. It will take care of the blow by created by the piston movement. Also removes some of the moisture created on a cold startup engine. I run a vacuum pump on the track and on the street. I find the pressure has to go somewhere and it likes to exit the rear seal. Tin Indian makes a nice mandrel setup for the crank pulley. I like the GZ vacuum pumps. Another option is evacs run off both valve covers to the exhaust. Normally done with open headers. Alot of folks at the track do this setup. Just remember that the engine has to be sealed up to run a vacuum pump.
https://www.tinindianperformance.com...%20systems.htm
https://www.gzmotorsports.com/

I've always heard you had to run open headers with valve cover evacs. Then my neighbor bought a 66 Impala that had them with a crappy 2.5" crush bent exhaust on a 11:1 454. When you took one of the breathers off at idle and put you hand over the hole it had very noticeable suction.
He put a pcv system on it and almost immediately it started having minor valve cover gasket leaks and the rear main started weaping. Reinstalled the evacs and they stopped. Just one example but in this case they worked perfectly with a full exhaust.

I had excessive blow-by that caused the same problems, and adding breathers just caused a mess. My quick successful fix was to keep the PCV (strictly for the purpose it was designed for) and add an evac to one valve cover (Moroso 68785, 23875, 97810 plus misc. hose etc.). Solved the immediate problem but eventually the oil consumption got out of hand and I had to tear the engine apart for a complete refresh. Your might not be as bad, and the evac might be all you need. Not a vacuum pump, but a quick low cost way to make some progress.

[QUOTE=steve25;6299956]Even if your ring seal is ok the pistons pump as much air volume around the crankcase as they draw in on there top side, and collectively they pressurize that air which then needs to go somewhere!

When each one of your pistons desend’s the bore of your 461, there also moving 57 cid worth of air!


I disagree.

For every piston going down into the crankcase there is a corresponding piston going up at the same time. This should cancel out the piston pressurizing the crankcase. The blowby is another thing altogether.

None of the circle track racing engine I built had a positive crank case ventilation system on it. Non of the other racers did either. No dipsticks were blown out.

I have/had similar issues with my car as it's highway use involves sustained rpm's above 3000. The engine also sat unused for about 15 years before I finished the car and I know its ring seal isn't the best as a result.

I was building enough pressure to push the dipstick out a bit and on long highway speed cruises it would puke a little oil out the dipstick as well.

Problem is the engine actually runs very well. It doesn't burn oil, doesn't smoke and makes the power that it should for it's combination (13.38@104 in 8500 DA).

So my solution was to ditch the PCV entirely. In high vacuum situations the valve is closed and you're using your heads to relieve crankcase pressure. So that high rpm cruising can cause problems if you've got poor ring seal.

I went with a Mighty Mouse Solutions draft setup. I use the factory location PCV grommet but instead plumb in a -8 AN fitting to the draft can. I have -8 AN line from the can to the back of the manifold and a single open breather in the driver's side head.

This setup provides up to about 800 hp worth of atmosphere relief at all times, not just under load. It's still a recirc situation so you're not putting these fumes back into the atmosphere unless the draft needs to open under heavy load. I use a Tomahawk valley pan with the stock style baffle. What oil the baffle doesn't remove, the draft can captures the vast majority of the rest.

Since I went this direction, I no longer get blow-by fumes on heavy acceleration in the cockpit, I'm not blowing out oil seals on the engine during high rpm cruises and the dipstick largely stays in place. I do still push the dipstick out on occasion but I honestly think that's also part of a function of its proximity to the crank. I haven't puked any oil out of the dipstick since the change.

I've put about 2500 miles on this setup now and have yet to need to empty the tank.

Attachment 579103

I'd argue that when one piston (let's say #1) is moving down to push 57 cid behind it into the crankcase another piston (#4) is moving upward at the same rate creating space for that 57 cid. So the air is just moving back and forth between the back sides of pistons. In a perfect engine (no blow by at all) you could theoretically have a closed crankcase.

Not that this really has anything to do with WakeSupremo's question.

If the air cleaner is a factory air cleaner, yes.

If the air cleaner is a open element air cleaner maybe.
I say that because there were some California 1966 Tri-Power GTOs
that had the fresh air intake for the crankcase attached to the bases of the Tri-Power air cleaners.
See photo below.

Tom V.

Thanks Tom.

OP - I bought a manometer and hooked it to my dipstick tube. I got some very different readings with two different PCV valves that seemed very similar, but the differences were consistent and repeatable. Maybe a manometer could help you diagnose your issue? I am chasing oil leaks but who knows, maybe if I fix them all I will start blowing out my dipstick too :D

The evac system might work on that Chevy at idle when it was checked, but the evac system needs to see vacuum and as engine RPM increases the vacuum present at the evac tube is going to turn into pressure with mufflers at which time the evac check valves close and they stop working until the engine returns to idle.

I don't run a PCV valve when breaking in an engine on the run stand because it's just one more variable that doesn't need to be dealt with during break-in. I leave off the breathers and stick on blue painters tape over the breather holes on both valve covers and take a razor blade and make one simple slit in the tape. During running between 2,000 and 2,200 that tape barely flutters. If something was wrong with ring seal the tape would split and be blown out. Luckily that hasn't happened.

I always thought the vacuum was created by the Venturi effect of the air rushing past the tube in the collector? Especially since the tube has to be installed and it’s end cut at the proper angle to work as it is supposed to. If that’s the case the the faster the gas speed across the tube the harder the draw.
A mediocre dual system might make 3-4 psi back pressure at load which is around 6-8in Hg. A good exhaust system 1-2psi. As long as your pulling more than that in the evac tube it should flow.

I agree with you on the analysis of the venturi effect, which is how that system was designed to work. Adding complete exhaust system with mufflers seems to throw things off. I believe that's what lust4speed is referring too. No cars I've ever seen at the track have full exhaust systems with evac setup.

At idle when the typical engine, 350 cid to 450 cid, consumes about 18 cfm of air to run at the typical idle rpm 850 to 1000 rpm.
Emissions engines can run less.

So the PCV Valve consumes typically from 2.5 cfm at WOT to 4 cfm during part throttle and cruise, (cruise is assumed to be 2000 rpm or more and about 250 cfm).
So that PCV valve ADDS "ONE ONE-HUNDREDTH" OF THE AIR FLOW TO THE ENGINE.

Doubt if that 2.5 cfm could even be noticed at idle and low speed on the dyno as most dynos are over 1000 rpm during a running engine test.

Last Point, Pontiac engines put on a engine dyno as there because the owners care about engine power,
not long term durability of the engine components due to the corrosive gases generated by the engine when running.

So do whatever makes you happy.

Tom V.

What I'm saying is that there is enough backpressure from street mufflers to easily slow the air movement past the evac pipe and kill any venturi effect. Open exhaust has plenty of air speed to make the system work properly.

I also agree that a properly functioning PCV valve is all positives. Only reason I don't run one on the initial startup and break-in is that it is a terrible time to find one of the many bad ones that try and suck the engine dry. Once the engine has the break-in time, then I toss on the PCV valve and check to make sure it's working correctly. Our group has had so many malfunctioning PCV valves that it's not worth the risk on the first startup. One of our members drove down to Harry K's for a dyno session and it looked like he was fogging for mosquitoes. We pulled the defective valve, did the dyno with some residual smoking, and by the time he drove home the engine was smoke free. The Chinese just don't have those sorted out, and like a lot of parts today we are the quality control point.

I run full 3.5" exhaust with header evacs on my 66 GTO race car that is also street driven. Been this way for over 20 years. Never an issue, I just take the valves out of the collector about 1x a year and spray some penetraing oil in them and check them.
If I don't run them it will push the dipstick out about 1 inch on a 7200/7400RPM run.